Detonation pickup



la -(mu SR m 29435.031 SEARCH ROOj j '7 i I I i i ,1948. J. R. BURNS ET AL 2,435,031

DETONATION PICKUP Filed Feb. 16, 1944 CROSS REFERENCE ZSmaentors W 1 7" v (Ittomegs 2435'u3 OR IN: 310/225: 7 1.

Patented Jan. 27, 1948 DETONATION rroxUP John R. Burns and John M. Whitmore,- Indianapolis, Ind., assignors to General Motors Cori poration, Detroit, Mich.,

- ware This invention relates to detecting means and more specifically to pick-up means or means for detecting knock or detonation in a closed engine cylinder through variations in internal pressure a corporation of Dela- Application February. is, 19 4, Serial No. 522,580

5Claims. (Cl.'171 209) tion and claimsand the illustrations in the accompanying drawings, in which the figure is a vertical section taken through a detector or pickup device of our invention.

therein. It is of course wellknown that the eX- Referring now more specifically thereto, there Plosive mixture within a cylinder upon bein is shown therein a portion of the cylinder Wall 2 fired under certain conditions causes knocks or which has a tapped opening 4 in the upper surundesirable pressure increases during certain face thereof in which is supported an attaching phases of operation of an internal combustion enmember 6 by means of an integral threaded stud gine. In some instances with the present high 10 8 on the lower surface thereof. The body of this speed and high power engines such knocking or plate is screw-threaded into the lower end of a detonation may seriously injure the engine if alroughly cylindrical body In forming the exterior lowed to continue for even a relatively short time. housing for the detector. Near the upper end of It is necessary therefore to study knocks or unthis body it is reduced in diameter to form a desirable detonations occurring within the engine shoulder 14 and the upper portion is externally cylinder during operation and also to be advised threaded as at l2 to support connecting means. as to the appearance of detonation within the Within the body In there is provided a disc cylinders when an engine is being normally op- IE having a cavity IS in its lower face and superated under load. porting upon the central portion of its upper sur- These knocks or detonations of course result in face an insulating plug 20. This insulating plug pressure changes within the cylinder and in the is secured to the disc l6 by suitable cap screws 22 past have been studied by providing somewhere and carries at its center an electrical contact 24. in the surface of the cylinder an opening into The attaching member 6 is also provided with a which was inserted means such as a diaphragm small recess 25 in its upper surface in substantial whose position would be altered through a change 25 alignment with the cavity I8 in the lower surface in internal pressure in the cylinder which moveof the disc I 6 and clamped between the two with ment would be proportional to the pressure causits ends lying in these recesses is a magnetostricing the knocking and would be detected by suittive member 23 which may be, for example, of able means. However, through the use of high such material as Alnico and possesses substantial compression fuels, such as are prevalent at the permanent magnetism. Mounted upon this magpresent time, the configuration and size of the net 28 is a coil form 30 supporting coil 32, one engine chamber has a great deal to do with flame terminal of which may be connected to contact pr p gation or explosion therein and any slight 24 and the other terminal may be grounded. The variation in either the size or shape of this chamattaching member 6 therefore may b tightly ber affects the operation or knock characterscrewed into the threaded aperture 34 in the istics thereof. Therefore, in order to obtain a lower end of the housing [0 and clamp tightly the detection of this detonation, it is desirable not to magnet 28 in the position shown brin it under disturb the contour or volume of the cylinder if some stress. possible. One end of a connecting cable 36 is shown It is therefore an object of our invention to 40 p d o t e supper end Of t e h us l2 by provide detecting means mountable on th x a threaded nut 33 which holds the ring integral t a Su a O a cylinder for investigating or with the end of the cable to the top surface of indicating internal Pressures therein the housing. A spring contact member 40 is S a further o l t Of our invention to p forced against the upper surface of the contact zl lde dztonaltionfdetectmg ln s mountaple on 24 to conduct current into the cable. When this mcevtizrilrgeggatssur ace 0 cy 1n er and having no construction is thus mounted on the external It is a still further object of our invention to surface-of a-cy-hnder vlbr-atmns caused by means time:stat s:satires:its; y a ig stricture means as the Sensitlve eleinternal magnet member 28 to vary, which will w these and other bj cts in View which will in turn vary the reluctance of this magnetobecome apparent as the specification proce d strictive member, altering the flux therethrough. the embodiments of our invention will be best un- This Variation in flux therefore induces current derstood by reference to the following speciflcain the coil, which current is in turn introduced into the connecting cable and may be conducted to suitable indicating means.

This device does not require any external power or energization as is necessary in the majority of other types of detonator pick-up devices, but since the change in reluctance is sufiicient, does not need supplemental power. Furthermore, it has no moving parts which might become broken or injured through operation or excessive vibration and is easily and simply constructed and therefore provides a very practical pick-up for this use. In operation the output of this pick-up may be introduced to a meter for accurate observation or may be merely connected to-a visual light source which will be energized upon detonation within the cylinder reaching a point where it might be destructive.

We claim:

1. In means for detecting detonation within an engine cylinder, a housing rigidly mounted on the external wall of said cylinder and having a rigid base subject to. the vibration thereof, a coil supported within said housing, a. magnetic core for said coil securely clamped under com pression within the housing on said rigid base and formed of magneto-strictive material so that the reluctance of the same will be varied by vibration and induce detectable current within the coil.

2. The combination of a rigid support adapted to be secured to the exterior surface of a. part subject to vibration, a magneto-strictive permanent magnet member of high retentivity seated upon said support, means engaging the opposite end of said member to hold it under compression and in contact with said support and forming with said support and member a closed magnetic circuit, a coil carried by said support and interlinked with the magnetic circuit whereby any change in the reluctance thereof will induce a current in the coil.

3. The combination of a non flexible base adapted to be secured to. the exterior surface of a cylinder of an engine, supporting means extending from said base, a magnetoestrictive member seated on the base in spaced relation to said supporting means, means engaging said supporting means and said member to hold the member under compression on the base and forming therewith a closed magnetic circuit, the

inertia of said parts causing a variation in the stress of the magneto-strictive member when the assembly is vibrated, and a pick-up coil mounted adjacent the member and affected by the varying reluctance caused by stress variation.

4. The combination of a non flexible base adaptedrtobesecured tothe exterior surface of a cylinder of'an, engine, a substantially cylindrical housing supported on said base, a bar of magneto-strictive permanent magnet material seated on the base, a block of magnetizable material engaging the outer end of the bar and the housing to clamp the bar under compression in position, and to form with the other members a closed magnetic circuit, a contact block of insulating material carried by the magnetizable block within, the housing and a pickup coil connected' to the contact block mounted in the housing in: juxtaposition to the bar to be afiected by a change in reluctance of the bar caused by stress change due to vibration.

5. The combination of a non flexible base adapted. to be secured to the exterior surface of a. cylinder of an engine said base having threaded sides, a substantially cylindrical housing. supported on said base in threaded relation, a bar of magneto-strictive permanent magnet material, seated on the base, a block of. magnetizable material engaging the outer end of the bar and the housing to, clamp the bar under compression in position and to form with the other members a. closed magnetic circuit, the initial stress in the bar being adjustable, as the housing is, screwed onto the base and a pick-up coil mounted around the bar within the housing to be affected by a change in reluctance of the bar caused by a stress change due to vibration.

JOHN R, BURNS.

JOHN M. WHI'I'MORE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,153,571 Kallmeyer Apr. 11, 1939 2,269,760 Eldredge Jan. 13, 1942 2,291,045 Lancor July 28, 1942 2,275,675 Draper et al Mar. 10, 1942 

